"Personal Velocity," which won the Grand Jury Prize at this year's Sundance Film Festival, is made up of three separate stories, each about a woman reaching a crisis in her life. Written and directed by Rebecca Miller, all the segments are stylistically similar, featuring raw-edged cinematography and an emphasis -- indeed, a dependency -- on narration. But the episodes, which star Kyra Sedgwick, Parker Posey and Fairuza Balk, respectively, vary in quality, and this discrepancy keeps the stories from having a cumulative impact.

Instead, "Personal Velocity" is a hit-and-miss affair, or, to be more precise, a miss (story one), hit (story two) and break even (story three) affair. Filmed on digital video, the movie looks a bit fuzzy throughout and occasionally indulges in Dogma-style photography, in which folks keep shaking the camera in the name of art. Still, there's no denying that Miller is ambitious in her attempt to delve into the psyches and motivations of three women. At its best, "Personal Velocity" has moments of illumination that can't be found in the average movie.

ON THE RUN

The first story makes for a dispiriting start. Sedgwick plays Delia, a wife and mother with a somewhat raunchy sexual history, who takes off with her kids after getting beaten by her husband. The episode plays as a kind of inadvertently condescending ode to white trash, with the woman -- who's nasty to everyone who helps her -- remaining opaque and somewhat repellent.

It's in the first episode that Miller's reliance on narration is most slavish and uncinematic. At times it feels like a short story with pictures, with actor John Ventimiglia intoning prose passages in voice-over that explain the inner life of the character. But it's worse than just a story with pictures, because the pictures are disappointing. We hear, for example, that the other residents of the battered women's shelter are intimidated by Delia's silence, but there's not a hint of that dynamic expressed visually.

Things get a lot better with the second story, in which Parker Posey plays Greta, a New York editor whose marriage is destabilized by her sudden success. The role of a Manhattanite who comes to adopt her estranged father's rapaciousness and emotional expediency turns out to be a fine showcase for Posey's nervous intelligence.

Posey made so many independent films in the '90s, some of them in unworthy roles she had to pull off through sheer bravado, that there may be a tendency not to realize that this an actress of subtlety and elegance. She may be a natural comedian -- high-strung and yet without neurosis -- and she's certainly funny in "Personal Velocity," dealing with a devoted, Lassie-like husband (Tim Guinee) and always, seemingly, stumbling and careening through life, unbalanced in her contacts with people.

But Miller gives Posey other internal moments, of rueful dignity, of regret,

of recognition of the inevitably of her own nature. No narration is needed for the moment when, without realizing, she abruptly smacks her husband's shoulder as he reads the morning paper. It could be a love pat. It could be an axe. It could be both. The truth and its complexity are in Posey's face.

COPING WITH TRAUMA

The last segment, starring Fairuza Balk as a pregnant 21-year-old woman who goes on a road trip in the aftermath of a traumatic accident, has the makings of something. Paula is so without direction that she sees everything that happens to her as a sign. Balk lends the character a live wire, damaged quality, and her watchfulness as an actress -- those big eyes that are always sensitive no matter how surly her expression -- feels right in a character who's always on the look-out.

But the story has the feel of a first draft, good in its outlines but meandering in execution and without a forceful pay off. So the segment, and the entire movie, ends with no velocity; it just trails off. Still, anyone who sees "Personal Velocity" will have a hard time forgetting Posey's performance.